Devices for protecting electrical installations are commonly used in particular for protecting electrical or electronic apparatus against surges that can be generated by lightning discharges, for example.
In general, such devices comprise an active portion formed by one or more protection components, such as a varistor or a spark gap.
Varistors are components commonly used for protecting electrical installations or equipment against transient voltage surges.
When a surge occurs within the installation, the varistor is subjected to a current shock that has the effect of degrading it and causing it to heat up, making thermal disconnection thereof necessary.
The degradation of a varistor is difficult or impossible to predict, insofar as it depends not only on the number of current shocks the varistor has suffered over its lifetime, but also on their amplitude.
Consequently, it is difficult to predict, a priori, the lifetime and the degree of aging of a varistor, and users often discover a posteriori that the varistor has been destroyed, such that the installation runs the risk of operating without any protection during some length of latency time.
In order to enable a defective varistor to be identified quickly and thus reduce the above-mentioned latency time, it is known to fit each varistor with indicator means suitable for informing a third party that the varistor is out of operation.
The varistors that are generally encountered are thus associated with disconnector means adapted to disconnect a varistor once it is in a degraded state and before it heats up excessively, which disconnector means are functionally connected to means for indicating the state of the varistor, that are generally actuated themselves by the disconnector means, and that serve to inform a third party whether the varistor is in operation or is disconnected.
The indicator means can thus be in the form of a slider associated with an indicator and suitable for moving in translation under drive from the disconnector means so that its position indicates the state of the varistor, with this being done by putting the indicator, e.g., a colored screen, in register with a viewing window formed in the housing of the protection device.
In known protection devices, the slider and the indicator are either secured to the disconnector means, in particular a disconnector blade, or else they are independent therefrom, while being controlled and actuated thereby.
In any event, moving the disconnector means towards their open position causes the slider to move in a manner that is controlled or guided by the disconnector means or by independent guide means.
Unfortunately, it can happen that the slider or the indicator is impeded in its movement, in particular when the slider and/or the indicator are poorly dimensioned or if the guide means are defective, thus leading to the slider being poorly guided.
In this situation, the slider and/or the indicator can impede or even prevent disconnection of the varistor. The varistor then remains connected and the indicator means do not indicate any abnormality in spite of the varistor being badly degraded, and in danger of causing a fire on being overheated.
In addition, configurations in which the slider and/or the indicator are actuated and moved under control by the disconnector means generally require the component parts to be accurately dimensioned, firstly so as to avoid slack arising between the parts, and secondly to avoid any risk of the disconnector and/or indicator system jamming.
In addition, in order to avoid the slider and/or the indicator slowing down disconnection, disconnector blades are generally designed in such a manner as to present a strong spring effect suitable for overcoming any braking effect exerted by the slider and/or the indicator.
Nevertheless, such a measure presents the drawback of weakening the soldered connection between the disconnector blade and the corresponding electrode of the varistor.
In general, the mechanical complexity of known devices requires the operations of manufacturing the parts to be very well controlled, thereby significantly increasing the cost of manufacturing such devices.
The above remarks naturally apply to devices that use other protection components, in particular spark gaps, in which it can be necessary in certain applications to make use of thermal disconnections.
It can thus be seen that there is a need to make a voltage surge protection device that, while being simple and inexpensive in design, is nevertheless capable, in the most reliable and effective manner possible, of disconnecting the protection component in the installation to be protected, and of simultaneously indicating to a third party that the protection component in question is out of operation.